The present invention relates to a brushless motor, which can be used, for example as an electric motor provided with a reduction mechanism for feeding paper money that has been inserted into a vending machine into a paper money transport path.
For example, Japanese Utility Model Registration Publication No. 2532489 describes a brushless motor covered by a frame (cover member). In this brushless motor an armature core (stator core) is fastened to the outside of an insulator (bearing holder), which is fastened to a printed circuit board (retaining plate), and a magnet (rotor magnet) that faces the outside of this armature core is fastened to the inner circumferential face of a rotor frame (rotor case). A rotary shaft that is fastened to the center of this rotor frame is supported by an oil-impregnated sintered bearing that is fastened to the center of the frame, and by an oil-impregnated sintered bearing that is fastened to the printed circuit board, and the top end of the rotary shaft protrudes from the frame.
However, in Japanese Utility Model Registration Publication No. 2532489, cumulative manufacturing variations in the dimensions of the parts result in large variations in the amount by which the rotor frame moves in the thrust direction (thrust play).
That is to say, the printed circuit board, the insulator and the armature core are each manufactured with tolerances in the axial dimensions of the parts and, in the assembly process, these tolerances are cumulative, such that there will be a greater dimensional tolerance in mounting the rotor frame, on which the magnet that faces this armature core is fastened, on the rotary shaft. Consequently, there will be great variation in the thrust play (gap in the thrust direction) between the rotor frame that is fastened to the rotary shaft and the oil-impregnated sintered bearing that is fastened to the center of the frame.